<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>

  <div id="app">
    <h1>{{firstName}} {{lastName}}</h1>
    <h1>{{fullName}}</h1>
  </div>

  <script src="./js/vue.js"></script>
  <script>
    const app = new Vue({
      el: '#app',
      computed: {
        fullName() {
          return this.firstName + ' ' + this.lastName
        }
      },
      data: {
        firstName: "Jone",
        lastName: "Brown"
      }
    })
  </script>
</body>
</html>